The invention relates to earth excavating and more particularly to the excavation of holes underlying existing building walls to permit underpinning to be constructed to support the building.
In order to construct underpinning beneath an existing building, holes must be excavated at least partially underlying the building wall to enable the underpinning to be placed under the wall.
In prior art technques for excavating underpinning holes, it has usually been necessary to perform a substantial amount of the excavation manually. First, a hole is usually dug contiguous to a building wall and as the excavation proceeds downwardly, it must be extended laterally under the bottom of the wall in order to accommodate the underpinning. The portion of the excavation which underlies the wall is difficult and inconvenient to perform by machine. As a consequence, it has generally been necessary to position laborers in the hole who remove the earth from beneath the wall by utilizing hand tools.
Such manual excavation is slow and expensive. In certain soil conditions, such as wet sand, manual digging is attended by a significant danger of cave-in or collapse. The conventional practice of reinforcing excavations by partial filling with drilling muds, such as bentonite slurries, cannot normally be employed when laborers are present in the excavation.